The invention relates to a heat exchanger, especially one for motor vehicles.
Such a heat exchanger is disclosed, for example, by DE 198 13 989 A1. This heat exchanger may take the form, for example, of a condenser for an air conditioning system for motor vehicles. Alternatively the heat exchanger may take the form, for example, of a radiator which serves for cooling the coolant of a coolant circuit in a motor vehicle. The heat exchanger has a number of flat tubes arranged side by side and running parallel to one another, that is to say tubes the cross-section of which is fundamentally rectangular. Flowing in these flat tubes is a first fluid, such as a coolant in the case of a radiator or a gaseous refrigerant that is to be condensed, in the case of a condenser for an air conditioning system. The flat tubes are connected to manifolds or collecting pipes and exposed to the flow of a second fluid, such as ambient air, in order to produce a transfer of heat between the fluids. Flow paths for the second fluid are formed between the spaced individual flat tubes.
In order to improve the heat transfer between the fluids, cooling fins are arranged between the flat tubes and fixed to the latter. In the heat exchanger disclosed by DE 198 13 989 A1, the surfaces of the cooling areas are fundamentally situated transversely to the direction of flow of the second fluid. This means that there is a considerable flow resistance to the second fluid. Designing the cooling fins to obstruct the flow is purposely intended to reduce the rate of flow of the second fluid. This, on the one hand, increases the time which the second fluid spends flowing through the heat exchanger, that is to say the time in which the second fluid can absorb heat from the first fluid or transmit heat to this. On the other hand, however, the low rate of flow of the second fluid limits the amount of heat transferable between the first and the second fluid, that is to say the efficiency of the heat exchanger.
A further heat exchanger with cooling fins is disclosed, for example, by U.S. Pat. No. 4,676,304. In this heat exchanger the cooling fins lie fundamentally parallel to the direction of flow of the second fluid (in this case, air). Despite the formation of baffle louvers on the individual cooling fins, it is nevertheless impossible to prevent some of the second fluid that flows through the heat exchanger from flowing between adjacent cooling fins without absorbing significant amounts of energy from these or giving off energy to these fins. This problem is particularly important when the heat exchanger has small dimensions in the direction of flow of the second fluid. In this case a high mass flow of the second fluid does not necessarily result in a high heat transfer coefficient. Only a relative small proportion of the available temperature difference between the first and second fluid is utilized.